Harbor Porpoise
One of the smallest of the oceanic cetaceans, the harbor porpoise is shy and elusive, not inclined to approach boats and bow ride, as many other species of dolphins and porpoises do. On calm days these animals can be easily detected by the loud puffing sound they make as they surface to breathe. Because of its inshore habitat, it is one of the best-studied small cetaceans, and also one of the most frequently hunted. Physical Description Are grayish- brown on their backs and sides, with white undersides. There are often gray stripes or flecks within the white pigmentation, especially in the throat region.A distinctive lateral grey – brown stripe extends from the corner of the mouth to the anterior insertion of the pectoral flipper on both sides of the animal. The width and pigmentation of this stripe varies among individuals, however is rarely visible on wild, healthy animals. Habitat and Diet Harbor porpoises are found throughout the temperate coastal waters of the Northern Hemisphere. As their name suggests, they prefer the shallows, less than 500 feet deep, and are commonly seen in harbors and bays. They are also known to frequent inland waters, including rivers, estuaries, and tidal channels. Harbor porpoises survive primarily on fish and are among the smallest of the cetaceans, reaching an average size of about 5 feet and 121 pounds. They can dive deep, more than 655 feet, but usually stay near the surface, coming up about every 25 seconds to breathe with a distinctive puffing noise that resembles a sneeze. Foraging Behavior Harbor porpoise feed on prey both within the water column and on the sea floor. They typically eat fish and squid between 10 – 25 centimeters in length. Like other odontocetes, they cannot chew, so they must swallow their prey in whole pieces. It has been proposed, that harbor porpoise may go for larger fish, but will attack them from behind and bite through them at the gills, ingesting the body without the head. Experiments at the Harderwijk rehabilitation center for stranded harbor porpoise in the Netherlands have shown that harbor porpoise actually create negative pressure in their mouths, using their tongues, to suck the fish into their mouths. This would reduce the likelihood that a live fish could escape. They also manipulate fish to swallow them headfirst. Some harbor porpoise have died by trying to eat prey that is too large to swallow. Differences With Other Dolphins Unlike their dolphin relatives, they have a blunt, rounded head rather than a prominent forehead and snout. Their mouths are short with black, inward-curving lips and spatulate, or spade-shaped, teeth. Their necks, short and immobile, are virtually undistinguishable from their grayish bodies, which taper to a tail with small, curved flukes and a middle notch. Reproduction Harbor porpoise give birth to one calf every year to every other year after a 10-11 month gestation period. Lactation lasts for approximately 9 months but calves will start to consume solid food at about 5 months of age. Calves may stay with their mothers for up to another 9 months post-weaning. Groups of 2 –3 animals are very common in British Columbia. It is possible that these groups are mothers with their growing calves. Reproduction is thought to be based on sperm competition, rather than competition between males for females. This is because the testes of a male harbor porpoise are exceptionally large during the reproductive season and may account for 4-6% of his body weight. This means that a 50kg male, will have approximately 2 kg testes! Conservation Because of their retiring nature, scientists know little about the behavior of these creatures in the wild, and much species research is focused on specimens rescued or killed as bycatch in fishing nets. In the Gulf of Maine region in the early 1990s, for example, as many as 3,000 were annually drowned in commercial fishing gear like gill nets. Populations are also harmed by chemical and noise pollution. Category:Mammals Category:Marine Mammals Category:Predators Category:Carnivores Category:Sea Creatures Category:Porpoises Category:Endangered Species